Rundown here:
http://kenstechtips.com/index.php/te...on-uk-networks
Giffgaff runs on O2 network and allows tethering if you've been happy with O2 coverage
https://community.giffgaff.com/t5/Le...y/ta-p/7816336
Giffgaff now send sims internationally (no 3rd party needed) and offers top ups with international credit cards
http://prepaid-data-sim-card.wikia.c...Availability_5
We’ve got more good news for you. Because we aim to make life easier, all international joiners will be offered the option of activating their giffgaff SIM, topping-up and auto-recurring their goodybag using an international credit card.
This idea was originally posted by william_li and brought back to life by gsklb04